A belt-type continuously variable transmission of a vehicle includes a primary pulley, a secondary pulley and a belt wound around the primary and secondary pulleys so as to change the widths of V-grooves between movable sheaves and fixed sheaves of the primary and secondary pulleys by axial movements of the movable sheaves relative to the fixed sheaves and thereby vary the speed ratio of the transmission. In general, the movable sheaves are actuated by hydraulic pressure. Hydraulic chambers (piston chambers) are thus provided on the back surface sides of the movable sheaves to apply hydraulic pressure to the movable sheaves.
The hydraulic chambers on the back surface sides of the movable sheaves are defined by structural members adjacent to the fixed and movable sheaves. There are sliding contact parts between these structural members. Seal members are arranged in the respective sliding contact parts so as to prevent oil leakage from the hydraulic chambers to the outside. Each of the primary and secondary pulleys is adapted to clamp the belt between the fixed sheave and the movable sheave and transfer power to or from the belt. The belt clamping force of the pulley depends on the hydraulic pressure of oil inside the hydraulic chamber. In order to avoid slippage of the belt, high hydraulic pressure needs to be applied to the hydraulic chamber. It is necessary to prevent oil leakage from the hydraulic chamber even under such high pressure conditions.
In the case of an idle-stop vehicle in which only an engine-driven oil pump is used as a hydraulic pressure source for pulleys of a continuously variable transmission, the oil pump is stopped and does not supply hydraulic oil to hydraulic chambers of the pulleys during idle-stop control. As the automatic stop time of the engine under the idle-stop control becomes long, the hydraulic oil gradually leaks from the hydraulic chamber through a sliding contact part of the transmission pulley. This leads to the entry of air into the hydraulic chamber. The entry of air into the hydraulic chamber makes it necessary to take time to fill the hydraulic chamber with hydraulic oil, which results in deterioration of startability.
Under the above circumstances, Patent Document 1 discloses a technique to prevent the entry of air into the hydraulic chamber from around a resin seal ring (seal member) in the sliding contact part of the transmission pulley. In the disclosed technique, the engine-driven oil pump is actuated by forcibly restarting the engine upon the lapse of a predetermined time period T from automatic stop of the engine. In particular, the time period T is increased with increase in oil temperature in view of changes in the amount of oil leaking from around the seal ring due to the temperature dependence of the resin. By such control, the entry of air into the hydraulic chamber of the transmission pulley is suppressed so as to avoid slippage of the belt at restart of the engine and ensure the startability of the vehicle.
In the technique of Patent Document 1, the engine is forcibly restarted to actuate the oil pump for prevention of the entry of air into the hydraulic chamber. However, fuel is consumed by forcible start of the engine. In terms of fuel efficiency, it is effective to stop the engine for a longer time. There is a demand to develop a technique capable of, even when the engine is stopped, preventing the entry of air into the hydraulic chamber of the transmission pulley.
It is conceivable to prevent the entry of air into the hydraulic chamber of the transmission pulley by the use of multiple seal members. The seal members, when used in a larger number, causes a larger sliding resistance against the sliding surface. The moving response of the movable sheave deteriorates with increase in sliding resistance, whereby the speed ratio of the transmission cannot be controlled properly due to deterioration of speed ratio control response. For this reason, it is desired to improve the ability of sealing the hydraulic chamber by sealing member while suppressing increase in sliding resistance.
The entry of air into the hydraulic chamber from through the seal area of the seal members occurs as the hydraulic pressure inside the hydraulic chamber and hydraulic system communicating therewith becomes decreased. The leakage of oil from the oil pump hydraulic pressure source is a cause of decrease in inside hydraulic pressure. Although the oil pump is driven to suck and discharge oil from an oil tank, the oil returns to the oil tank under its own weight during stop of the oil pump to cause decrease in the hydraulic pressure inside the hydraulic system. With such decrease in hydraulic pressure, outside air enters through the seal area of the seal members.
The characteristics of oil return to the oil tank vary depending on the kind of the oil pump. In the case of a gear pump, for example, a part of gear in the pump case is held in contact with an inner wall of the pump room during stop of the pump so as to suppress the return of oil to the oil tank and prevent the entry of air into the hydraulic chamber. In the case of a vane pump, on the other hand, ends of the vanes are separated from an inner wall of the pump room during stop of the pump so as to cause the early entry of air into the hydraulic chamber without being able to suppress the return of oil to the oil tank. It is thus more desired to improve the ability of sealing the hydraulic chamber during stop of the oil pump in the case where the oil pump is of the type, like vane pump, that causes the early entry of air into the hydraulic chamber during stop of the pump.
The present invention has been made to solve the above problems. It is an object of the present invention to provide a vehicle continuously variable transmission with a seal mechanism capable of improving the ability of sealing a hydraulic chamber of a transmission pulley, or an oil passage communicating with the hydraulic chamber, by seal member even during stop of a pump while suppressing increase in sliding resistance. It should be understood that: the object of the present invention is not limited to the above; and it is also an object of the present invention to achieve any of features and effects by the respective configurations of the after-mentioned embodiment, which cannot be achieved by conventional techniques.